Allowable limits of particulates and noxious gases produced by internal combustion engines, including those produced by diesel engines, are generally regulated by government agencies. Manufacturers of such engines have accordingly devised techniques for controlling exhaust emissions. Many engines typically include an exhaust system particulate filter or trap, e.g., a soot filter. Particulate filters are generally designed to collect particulate emissions within the exhaust stream and either continuously or periodically burn off the collected particulates in a particulate filter regeneration mode. During a particulate filter regeneration mode, the temperature within the filter is preferably above a specified regeneration temperature to ensure thorough burning of the collected particulates. Additionally, performance of other exhaust gas treatment components, e.g., catalytic converters, may be improved above specified temperatures.
Particulate filters include active and passive types. Active particulate filters typically include one or more heaters for filter regeneration, and passive particulate filters typically rely on the temperature of the exhaust gas itself to sufficiently elevate the filter temperature for filter regeneration. Particulate filters are usually designed such that normal operation of the engine produces exhaust temperatures at or above a desired temperature to enable filter regeneration. However, under certain engine operating conditions, such as extended periods of engine idling and sustained operation at high engine speeds or low output torque, exhaust gas temperatures produced may be below the filter regeneration temperature and may adversely affect filter regeneration. As a result, particulate filters may frequently become clogged or plugged, thereby requiring unscheduled vehicle maintenance in order to clean the clogged or plugged filter. Additionally, particulate filter clogging or plugging may also result in filter failure through generation of excessive temperatures internal to the filter when soot is burned.
As shown in U.S. Pat. No. 6,427,436 (the '436 patent), a filter system can be used to remove particulate matter from a flow of engine exhaust gas before a portion of the gas is fed back to an intake air stream of the engine. Specifically, the '436 patent discloses an engine exhaust filter containing a catalyst and a filter element. A portion of the filtered exhaust is extracted downstream of the filter and is directed to an intake of the engine through a recirculation loop.
Although the filter system of the '436 patent may protect the engine from an amount of harmful particulate matter, the catalyst may convert sulfur present in the exhaust gas to sulfate. The sulfate may combine with condensed water to form sulfuric acid in the recirculation loop. The recirculation of sulfuric acid may corrode components of the system over time and may hinder the effectiveness and longevity of the system. In addition, the system of the '436 patent may not be capable of regenerating the filter element to remove particulate matter and other exhaust components trapped therein.
The disclosed system is directed to overcoming one or more of the shortcomings set forth above.